University of Tehran Public Law Studies Quarterly 2423-8120 51 2 2021 06 22 The Interplay between the Legislative Power of States with Foreign Investors Legitimate Expectations The Interplay between the Legislative Power of States with Foreign Investors Legitimate Expectations 431 454 80108 10.22059/jplsq.2019.272603.1892 FA Arash Behzadi Parsi Ph.D in public international law, Department of public & international law, faculty of divinity, political science and law, Science and Research Branch Islamic Azad University, Tehran, Iran Seyed Jamal Seifi Member of Iran- United States Claims Tribunal, Associate Professor National University, Tehran, Iran, Academic tenure holding visiting chair at Tilburg University, Tilburg, Netherlands Journal Article 2018 12 29 The power of States to alter their laws and regulations in a way that no harm is inflicted on foreign investor's rights, has always been one of the challenging issues under international investment law. One the one hand, the foreign investor expects that the laws and regulations of the host State remain unchanged in the course of his investment, but on the other, the efficient administration of society requires the amendment of laws and regulations based on the society's ruling circumstances. The interplay between the two above-mentioned trends, is subordinate to various factors. Hence, this article deals with the question that what role, the legitimate expectations of an investor, play with regard to the consistency of the laws and regulations of States. Applying analytical and descriptive method and by examining treaties and the awards rendered by investment arbitral tribunals, attempt is made to demonstrate that the legitimate expectations of investor may have a direct impact upon the host State's legislation discretion and entitles the investor to certain rights. The power of States to alter their laws and regulations in a way that no harm is inflicted on foreign investor's rights, has always been one of the challenging issues under international investment law. One the one hand, the foreign investor expects that the laws and regulations of the host State remain unchanged in the course of his investment, but on the other, the efficient administration of society requires the amendment of laws and regulations based on the society's ruling circumstances. The interplay between the two above-mentioned trends, is subordinate to various factors. Hence, this article deals with the question that what role, the legitimate expectations of an investor, play with regard to the consistency of the laws and regulations of States. Applying analytical and descriptive method and by examining treaties and the awards rendered by investment arbitral tribunals, attempt is made to demonstrate that the legitimate expectations of investor may have a direct impact upon the host State's legislation discretion and entitles the investor to certain rights. https://jplsq.ut.ac.ir/article_80108_d53add6ab3aba3db7b879204931391c6.pdf